Chlorinated polyolefins have been widely used as impact modifiers in polyvinyl chloride (PVC) compositions to form a composition that is less prone to failure on impact. For example in U.S. Pat. Nos. 3,006,889 and 3,209,055, the use of a broad range of chlorinated and chlorosulfonated polyethylenes in blends with PVC is disclosed. Elastomeric ethylene copolymers such as ethylene/alpha-olefin copolymers also have been used as impact modifiers. For example, in U.S. Pat. No. 5,925,703 Betso et al. teach the use of linear ethylene/alpha-olefins to improve impact performance of filled thermoplastic compositions, including polyvinyl chlorides. More recently, impact modifiers that are mixtures containing chlorinated polyethylenes and elastomeric ethylene copolymers have been taught. For example, U.S. Patent Applications 2003005040, 2003014442 and 2003015368 teach improved impact resistance PVC compositions comprising impact modifier blends of randomly chlorinated polyethylene and polyolefin elastomers. Also in U.S. Pat. No. 6,124,406 Cinadr et al. teach that blocky chlorinated polyethylenes can be used to compatibilize polyolefin elastomers and PVC to give a PVC composition with improved impact resistance.
Chlorinated polymers and polyolefin elastomers, as used in the previously mentioned applications are typically in the form of particulate solids. The use of these materials requires consideration of the solid handling aspects such as packaging, transporting, storing, and unpackaging these particulate solids. When handled as individual components, both chlorinated polyolefins and polyolefin elastomers exhibit varying degrees of particle agglomeration, also known as blocking, massing, or caking. These agglomerated products are undesirable. Extended warehouse storage or shipping time, especially during warm weather months, can exacerbate product massing issues. Botros noted that material handling problems for tacky ethylene vinyl acetate pellets become more severe at elevated temperatures during summer months and in large shipments where the pressure on pellets increases in Factors Affecting Antiblock Performance of Ethylene Vinyl Acetate Copolymers, Journal of Plastic Film and Sheeting, Vol. 11, pp 326–337 (1995).
As pointed out by Griffith in Cake Formation in Particulate Systems, VCH Publishing, 1991, “any industry producing powdered solids . . . cannot consider their products as Quality Products if those products arrive at the customer's home, plant, or worksite caked and lumped to the degree that the product is not ready for immediate use.” Agglomerated solids can cause such issues as interrupted schedules, scrapped or reworked product, and customer aggravation.
Numerous mechanisms can potentially cause particle agglomeration or caking. Griffith divided caking mechanisms into four major classes—electrical, chemical, mechanical, and plastic flow. Electrical behaviors that contribute to caking include static electricity and electrical interactions from crystalline structures. Chemical behaviors such as hydration and crystallization can also cause caking. Mechanical caking can be caused by particle entanglement. Plastic flow caking occurs when amorphous or soft crystalline substances merge after being subjected to either pressure or increased temperature. In the most severe case, the particles can flow together and form a single mass.
Griffith teaches that flow conditioners or anti-cake agents can be added to prevent particle agglomeration. One class of these is derived from organics such as amines, alcohols, acids, or salts. These materials form a barrier around particles and exhibit surfactant or lubricating effects. Another example of an organic anti-cake agent is disclosed in Japanese Granted Patent No. 90049207, wherein a polyoxyethylene surfactant was used to prevent blocking of chlorosulfonated polyethylene chips.
Fine-powdered solids that form physical barriers around particles can also be used as anti-cake agents. Examples include fumed silica, clays, talc, magnesium carbonate and polyethylene powders. In European Granted Patent No. 100434, Bohm et al. incorporated an anti-cake agent such as carbon black or finely divided phenolic resin, to prevent agglomeration of unvulcanized rubber particles such as alpha-olefins and chlorinated elastomers. In European Patent Application 410914, McCoskey et. al. generated pourable particles from normally tacky plastics by contacting the polymer melt with a cooling fluid containing a non-sticky material and subsequently re-contacting the plastic particles with a second non-sticky material. McCoskey showed improvement in caking behavior of propylene polymers by adding polyethylene powder to both the pellet water and to the finished polymer. Polyethylene powders having an average particle size of less than 10 microns have also been used as an anti-caking agent for vinyl acetate pellets in U.S. Pat. No. 3,258,841.
A combination of antiblocking agents such as organic dispersants and solid additives have been used to prevent agglomeration during chlorinated polyethylene manufacturing. For example, in U.S. Pat. No. 4,562,224 Busch et al. teach a process to produce chlorinated polyethylene in which poly-N-vinyl pyrrolidone and silica are present in the dispersant during the chlorination process. In PCT Application WO 01/12716, McMichael et al. teach a process of heat treating ethylene copolymer pellets and applying a talc anti-cake agent and a siloxane binding agent to generate substantially free-flowing pellets.